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Biochemistry > Muscle Physiology > Flashcards

Muscle Physiology Flashcards

1
Q

Skeletal muscle makes up what percent of nonfat body weight of the human body?

A

40%

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2
Q

How can muscles maintain body temp in response to cold? (shivering)

A

increases metabolic rate

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3
Q

What structures are responsible for the striation of skeletal muscle?

A

sarcomeres

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4
Q

Order of events in skeletal muscle contraction (9 steps)?

A

1) AP initiated/propagated through motor neuron
2) AP triggers ACh release at presynaptic membrane of neuromuscular junction
3) ACh diffusion to postsynaptic membrane in muscle fiber
4) depolarization occurs as a result of Na+ influx > K+ efflux
5) End Plate Potential triggers AP in skeletal muscle cell, propagates into t-tubules
6) AP triggers Ca2+ release from SR
7) Ca2+ binds to troponin, shifts tropomyosin to expose myosin binding sites
8) myosin heads bind to actin, causes shortening and contraction
9) Ca2+ falls, is pumped back into SR, relaxation occurs (ATP-dependent)

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5
Q

How many seconds of intense muscle activity does free cytosolic ATP provide?

A

5-6 seconds

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6
Q

What are 3 adequate sources of ATP for muscle contraction?

A

Creatine phosphate = 1 ATP per CP
Glycogenolysis (anaerobic respiration) = 2 ATP per glucose; lactic acid also a product
Cellular (aerobic) respiration = 38 ATP per glucose; CO2 and H2O also products

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7
Q

Energy source of ATP production in creatine phosphate?

A

creatine phosphate

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8
Q

Energy source of ATP in glycogenolysis/ anaerobic respiration?

A

glucose

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9
Q

Energy source of ATP in cellular/aerobic respiration?

A

glucose, pyruvic acid, free fatty acid, amino acid

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10
Q

Why do we breathe so hard after strenuous exercise?

A

We breath hard after strenuous exercise to get the extra oxygen that must be used in the oxidative energy processes to reconvert lactic acid to glucose and to restore the decomposed ATP and creatine phosphate to their original states

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11
Q

What is a muscle twitch?

A

the single, brief contraction of a muscle in response to a single AP on its motor neuron

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12
Q

Describe the “all-or-none” response of motor units (twitch)

A
  • When the motor neuron fires, all of the muscle fibers innervated by its nerve (muscles in that motor unit) will contract
  • Motor units contract and relax in an all-or-none manner
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13
Q

4 phases of skeletal muscle twitch

A

1) latent period - delay between stimulus and onset of twitch
2) contraction phase - period during which tension develops and muscle shortens
3) relaxation phase - loss of tension and return of muscle to resting length
4) refractory period - muscle will not respond to new stimulus

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14
Q

What is multiple motor unit summation/recruitment?

A
  • increasing the strength of the stimulus at a constant frequency to recruit additional motor units and thereby increase the tension developed
  • this is an example of graded muscle response
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15
Q

What is multiple motor unit summation/recruitment?

A
  • increasing the strength of the stimulus at a constant frequency to recruit additional motor units and thereby increase the tension developed
  • this is an example of graded muscle response
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16
Q

What is wave/temporal summation?

A
  • the result of a sustained contraction due to secondary twitch (summated tension) before initial twitch has fully relaxed
  • think of a staircase
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17
Q

What is treppe?

A

-a form of incomplete fusion of the wave summation at a frequency just below tetanus, but still below max tension

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18
Q

What is tetanus?

A
  • complete fusion of wave summation, or not relaxation between stimuli (result of depleting calcium)
  • remember Ca2+ is needed to process glycogen and to restore ATP, so prolonged tetanus can cause permanent muscle damage
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19
Q

What is muscle fatigue?

A

-the result of exhaustion of ATP, buildup of waste products such as lactic acid, and loss of tension despite continuing stimuli

20
Q

Tension vs load

A
  • tension is the force exerted on an object by a contracting muscle
  • load is the force exerted on the muscle by an object
  • thus, to shorted the muscle and move the load, the tension generated by the muscle must exceed the load from the object
21
Q

What is an isotonic contraction?

A

-sufficient tension to shorten muscle

22
Q

What is an isometric contraction?

A

-insufficient tension to shorten muscle, so muscle doesn’t shorten

23
Q

What occurs at optimal sarcomere length?

A
  • maximum overlap of myofilaments
  • maximum number of crossbridges
  • generates maximum amount of tension
  • (80-120% sarcomere length; lower limit 170%)
  • beyond upper and lower limits, negligible tension develops
24
Q

What is fractionation?

A
  • all motor units in a muscle do not need to activate for every load
  • more motor units = larger motor units recruited = greater tension developed
25
Q

What is Henneman’s “Size Principle”?

A
  • motor units are recruited in the order of the size of the motor unit based on the force/resistance needed
  • smaller to larger
26
Q

Describe the size principle in relation to recruitment of different sized motor units

A
  • motor units are recruited from smallest to largest
  • low intensity - type I (slow twitch) motor units
  • increased load - type IIa (fast twitch) are recruited to supplement type I fibers
  • even greater load - type IIb fibers recruited to supplement other recruited fibers
27
Q

Describe type I muscle fibers

A
  • slow twitch

- low-intensity

28
Q

Describe type II muscle fibers

A
  • fast twitch

- increased loads

29
Q

What is a reflex arc?

A
  • simple neural pathways connecting receptors to effector organs
  • responses generated are called reflexes, or reflex arcs
30
Q

Are reflex arcs somatic or autonomic?

A

Both

31
Q

6 basic components of most reflexes

A

1) a sensory receptor
2) an afferent neuron
3) an integration center (CNS)
4) an interneuron
5) a motor (efferent) neuron
6) an effector (muscle)

32
Q

What are somatic reflexes?

A
  • mediated by the spinal cord and can be used to fine tune muscle tone to do everything from maintain posture to preventing injury
  • occurs in skeletal muscle
33
Q

Stretch reflex (spinal reflex)

A
  • initiate at muscle spindles, which are sensitive to length of muscle as it is stretched
  • alpha motor neuron activated by stretch
  • stretched muscle is stimulated to contract (resist being stretched further
  • sensory receptors are proprioceptors
  • knee jerk reflex
34
Q

What is reciprocal inhibition?

A

When a stretch reflex stimulates a stretched muscle to contract, antagonist muscles that oppose the contraction are inhibited via a process called reciprocal inhibition

35
Q

What is reciprocal innervation?

A

the neuronal mechanism that causes reciprocal inhibition

36
Q

What are two subtypes of skeletal muscle fibers?

A

extrafusal fibers and intrafusal fibers

37
Q

What are extrafusal fibers?

A
  • make up the bulk of muscle

- innervated by alpha-motor neurons

38
Q

What are intrafusal fibers?

A
  • encapsulated in collagen sheaths to form the muscle spindle
  • innervated by gamma-motor neurons (and the afferents of group Ia and II sensory neurons)
39
Q

2 subtypes of intrafusal fibers

A
  • nuclear bag fibers

- nuclear chain fibers

40
Q

What are nuclear bag fibers?

A
  • subtype of intrafusal fibers
  • detect fast, dynamic changes in muscle length and tension
  • innervated by group Ia afferents (fast)
41
Q

What are nuclear chain fibers?

A
  • subtype of intrafusal fibers
  • detect static changes in length and tension
  • innervated by slower group II afferents as well as the fast group Ia afferents
42
Q

What is the golgi (deep) tendon reflex?

A
  • a protective feedback mechanism to prevent tendon damage
  • tendon reflexes are initiated at receptors in golgi tendon organs
  • GTOs depolarize in response to the tendon being stretched, but inhibit the alpha motor neuron
  • stimulates the contracted muscle to relax, relieving tension on the tendon
  • it is disynaptic
43
Q

Which two sensory organs fine-tune muscle tone?

A

muscle spindle (measures muscle length) and golgi tendon organ (measures muscle tension)

44
Q

What is the relationship between fine movements and number of muscle spindles?

A

-the finer the movement required, the greater the number of muscle spindles in a muscle

45
Q

Compare number of synapses, stimulus, and responses of the stretch reflex, golgi tendon reflex, and flexor withdrawal

A
  • stretch: monosynaptic, muscle is stretched, contraction of muscle
  • golgi tendon reflex: disynaptic, muscle contracts, relaxation of the muscle
  • flexor withdrawal: polysynaptic, pain, ipsilateral flexion and contralateral extension

Biochemistry (32 decks)

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